1. Field of the Invention
The present invention relates, in general, to an automatic tool changing device for NC machine tools and, more particularly, to an automatic tool changing device for machining centers, the device being positioned at a side of the movable table of a machining center and effectively changing tools within the inner diameter circle of a rotary housing, thus shortening the arbor movement stroke and saving tool changing time during a tool changing operation, the device being also effectively protected from the machining part or the spindle stock of such a machining center, thus being almost completely free from any damage caused by chips from the machining part.
2. Description of the Prior Art
As well known to those skilled in the art, machining centers are NC (numerical control) machine tools for shaping, cutting, milling, turning, boring, drilling, grinding, or polishing of solid parts, especially metals, under computer numerical control by making use of several axes and a variety of tools and operations. The construction of a typical machining center is shown in FIG. 7.
As shown in the drawing, the typical machining center comprises a bed 11, with a table 111 being carried on the bed 11 to be horizontally movable along an X-axis of the bed 11. A column 12 is positioned in back of the bed 11 to be vertically movable along a Y-axis of the bed 11. A spindle stock 13 is positioned in front of the bed 11 to be horizontally movable along a Z-axis of the bed 11, with a tool carrying arbor 100 being fixed to the stock 13. An automatic tool changing device (ATC) 9 is set on a side of the column 12 and is used for automatically changing tools for the spindle stock 13.
The construction of such a typical ATC is shown in FIGS. 8a and 8b in detail.
As shown in the drawings, the typical ATC 9 comprises a rotary tool carrier 91. The rotary tool carrier 91, set on a side of the column 12, is designed for being rotatable around its center shaft 911. An arbor position changer 92 is positioned under the rotary tool carrier 91 and is used for changing the position of a tool carrying arbor 100 from its horizontal position to its vertical position. A tool changer 93 is positioned at a side of the arbor position changer 92 and is used for moving the arbor 100 to the spindle stock 13 prior to changing an existing tool of the stock 13 with a new tool or the tool of the above arbor 100.
When it is necessary to change an existing tool of the stock 13 with a new tool using the above ATC 9, the tool carrier 91 is rotated around its center shaft 911 so as to allow the ATC to select a desired arbor 100 from a plurality of arbors 100 provided on the carrier 91. Of course, the arbors 100 individually carry a tool, so that the number of arbors 100 is determined by the number of tools for the machining center. The selected arbor 100 is, thereafter, horizontally laid on the center under the tool carrier 91 prior to being positioned vertically by the arbor position changer 92. The ATC 9 moves the vertically positioned arbor 100 to the spindle stock 13 by the tool changer 93 prior to changing the existing tool with the tool of the selected arbor 100.
However, such an ATC 9 is problematic in that it performs an automatic tool changing operation at the outer diameter circle of the rotary tool carrier 91, thus rendering the arbors 100 to move in a long stroke during a tool changing operation. This results in consumption of time during such a tool changing operation.
Another problem experienced in the typical ATC 9 resides in that it is positioned above the machining part of the machining center at a side of the column 12. The ATC 9 may be thus easily damaged or broken by the chips from the machining part.
In the prior art, the ATC 9, which is set on the column 12 to project outwardly, is covered and protected by an ATC casing. However, in order to effectively protect the ATC 9, the ATC cover has to be designed for having a large volume and this increases the manufacturing cost of such machining centers.